This invention relates generally to heat pump systems and, more particularly, to refrigerant expansion arrangements for heat pump systems with multiple fan coil units.
Conventional heat pump systems include the use of an expansion device with each of the two heat exchanger coils. During the cooling cycle the expansion device leading to the indoor coil is active to expand the refrigerant flowing to the indoor coil acting as an evaporator and, during the cooling cycle the other expansion device is active to provide expanded refrigerant to the outdoor coil acting as the evaporator. In either case, the inactive expansion device is effectively removed in the one direction by a bypass circuit. An example of such a system is shown in U.S. Pat. No. 3,992,898 issued to Duell, et al. on Nov. 23, 1976 and assigned to the assignee of the present invention.
A recent development is the so-called multizone heat pump system wherein, rather than having a single indoor or fan coil with a single outdoor coil, a plurality of fan coils are driven from a single outdoor coil. In this way, the fan coils may be selectively located in the various rooms of a building to more effectively meet the heating and cooling distribution needs within the building.
More often than not, the multiple fan coils within a single system are not at the same elevation. That is, while there may be one or more units on the main floor level, there is likely to be one or more units on an upper or lower level. Such an arrangement creates a problem with respect to the flow of liquid refrigerant, since the difference in elevation will tend to reduce the flow of refrigerant from the lower elevational fan coil(s) to thereby reduce their capacity, and possibly render them completely ineffective as the lower coils fill with condensed liquid refrigerant.
Another problem associated with multizone systems is that related to flow rate requirements for different sized fan coils. For example, assuming that the various fan coils are on the same elevational level, if one fan coil is larger than the other(s), it will need to pass a greater volume of liquid refrigerant than the other(s). If its flow volume is restricted to substantially that of the other unit(s), as will be the case where the units are all fluidly connected to a common refrigerant line leading to the outdoor coil, then the liquid refrigerant will tend to build up in the larger coil to thereby reduce its capacity.
It should be recognized that, to some extent, the above mentioned problem with respect to different sized coils will be self correcting. That is, as the liquid refrigerant volume builds up and is therefore elevationally higher in the larger coil, the associated increased pressure at the common points will cause a greater flow rate from that coil to thereby reduce the buildup. However, if the coils are on different elevational levels as discussed hereinabove, the self correcting phenomena may not occur and, in fact, the problem may be made more severe: i.e. where the larger coil is at the lower elevation.
It is therefore an object of the present invention to provide a multizone heat pump system with enhanced refrigerant flow characteristics.
Another object of the present invention is the provision in a multizone heat pump system for easily and efficiently accommodating fan coils at different elevational levels without incurrring differential flow problems.
Yet another object of the present invention is the provision in a multizone heat pump system for easily and efficiently accommodating fan coils of different sizes without incurring differential flow problems.
Yet another object of the present invention is the provision for a multizone heat pump system which is economical to manufacture and extremely functional in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.